1. Field of the Invention
The present invention relates to a reluctance-type electric motor.
2. Description of the Related Art
In general, a multi-phase reluctance-type motor is controlled by a driver circuit as shown in FIG. 1A. The driver circuit includes a CPU and processes sensor signals delivered thereto from the multiple-phase reluctance-type motor. Such a reluctance-type motor is simple in structure and provides a comparatively large output torque. However, it has been used in limited fields because of its high torque ripples.
As shown in FIG. 1B, a phase coil of a reluctance-type motor is usually supplied with drive current when a salient rotor-pole and a salient stator pole come across each. other and the inductance thereof starts to increase. The current supply is stopped when the inductance does not increase.
The current that is supplied to the coil gradually increases after the rotor salient pole and the stator salient pole come across each other and gradually decreases when the increment angle of the inductance changes near its peak. Therefore, the torque provided by the salient poles changes gradually. In other words, the torque characteristic is not flat. This mainly causes the above-stated torque ripples.
A main object of the invention is to provide an improved reluctance-type motor that generates a flat torque so as to reduce the torque ripples.
According to a main feature of the invention, a reluctance-type motor includes a stator having a plurality of salient stator-poles, a rotor having a plurality of salient rotor-poles, a multi-phase coils mounted in the stator, and a driver circuit for driving the multi-phase coil. The driver circuit starts to supply drive current to one of the phase coils when the salient rotor-poles and the salient stator-poles having the one of the phase-coils come across each other, while the inductance thereof is zero. Preferably, the driver circuit stops supplying the drive current before the increment angle of the inductance changes.
In the above-stated reluctance-type motor, the salient stator-poles and the salient rotor-poles are formed of laminated sheets of magnetic material and have a plurality of slits. The width of the slot is, preferably, equal to or larger than one fifth of the thickness of the laminated sheet.